The invention relates to a sliding bearing for supporting a rotation shaft.
A sliding bearing for rotatably supporting a rotation shaft, for example, a crank shaft etc. in an internal combustion engine is provided with a structure in which two bearing metal pieces of semicylindrical shape are combined along an inner periphery of a housing into a cylindrical shape. In the structure there is fed a lubricant oil between the inner peripheral face of each of the bearing metal pieces and the rotation shaft so that a lubricant film may be formed therebetween. By the lubricating and cooling effects of the lubricant oil, wear and seizure are restrained, and another effect of restraining noise is also brought about from the cushion function of the lubricant oil. The thicker the thickness of the lubricant film is and/or the more the amount of the lubricant oil is, the more the restraining effects become.
There are many conventional bearings in each of which a lot of fine grooves of several microns in depth are formed to be juxtaposed in an circumferential direction on an inner peripheral face of the bearing, so that the inner peripheral face is made to have an uneven surface in an axial direction. By means of lubricant oil contained in the fine grooves, the quantity of the lubricant oil is made to increase. For example, in JP-A-59-73620 Publication (prior art 1) there is disclosed a sliding bearing in which many fine grooves are formed to extend at an inclination angle of 0 to about 5.degree. regarding a circumferential direction while being spaced equidistantly apart from each other in an axial direction, by which structure it becomes possible to feed much lubricant oil in the fine grooves and to promote the dissipation of heat. In each of JP-U-63-53922 Publication (prior art 2) and JP-U-63-62621 Publication (prior art 3) there is disclosed a sliding bearing in which fine grooves extending on the inner peripheral face of the sliding bearing in the circumferential direction thereof are made to have a larger pitch in each of axially terminal end portions than that in an axially inner portion. By this structure it becomes possible to decrease the number of the fine grooves in the terminal end portions where misalignment occurs in relation to a rotation shaft supported by the bearing, and the decrease in area for supporting shaft load, which decrease is caused because of the providing of the fine grooves, can be restrained as little as possible to thereby make specific load onto the load-supporting area smaller, so that the lowering of endurance of the bearing is restrained. In JP-U-4-63809 Publication (prior art 4) there is disclosed a sliding bearing in which fine grooves are circumferentially formed only on crush reliefs which are provided in both circumferential ends of each of bearing metal pieces. By this structure in which the side of the fine grooves acts as dams, it is possible to restrain lubricant oil from flowing outwardly and to restrain oil feed pressure from being lowered.
In each of the prior arts, the inner peripheral face is made to be uneven (,i.e, not flat) in an axial direction so that the side of the fine grooves acts as dams for restraining the axial effluence of the lubricant oil, whereby the effluence of the lubricant oil and the lowering of the oil-feeding pressure are restrained while promoting the dissipation of heat. However, the forming of the fine grooves on the inner peripheral face makes the shaft load concentrated on convex portions defined between the fine grooves, with the result that wear resistance is lowered. Even in the cases of the prior arts 2 and 3 where the number of the fine grooves is decreased only in the end portions onto which more load is applied due to the misalignment of a rotation shaft, the lowering of the wear resistance can not be prevented.